Vehicles, including on and off-highway haul and vocational trucks, wheel loaders, motor graders, and other types of heavy machinery generally include a multi-speed, bidirectional transmission coupled to an engine. Such engines also typically include an engine retarder used to increase the natural resistance of the engine when braking is needed. For example, such engine retarders may include an engine brake or an exhaust brake configured to generate braking torque in braking situations. Such braking torque may supplement a braking force applied by the vehicle brakes, to assist in slowing and/or stopping the vehicle. Such braking torque may be required, for example, to slow or stop the vehicle on a relatively steep downward slope, to avoid overheating of the vehicle brakes, or in other situations where the force applied by the vehicle brakes is not sufficient to stop the vehicle as desired.
Such vehicles also include a variety of components directly or indirectly powered by the engine. For instance, one or more fans, motors, pumps, and/or other like components may be coupled to an output of the engine, and such components may be utilized to perform, for example, engine cooling, power steering, hydraulic implement actuation, and/or other like functions during operation of the vehicle. Such components may also be activated in conjunction with the engine retarder to provide additional braking torque in braking situations. This additional braking torque may assist in further reducing vehicle and/or engine speed.
One method of improving vehicle braking is described in U.S. Pat. No. 5,921,883 (“the '883 patent”) issued to Bellinger on Jul. 13, 1999. The '883 patent describes a braking system including an engine brake connected to an engine of a vehicle. The engine brake is operable to provide a retarding torque based on the gear ratio, vehicle speed, and/or coasting mode of the vehicle. The '883 patent also describes an engine cooling fan configured to provide additional retarding torque. The engine cooling fan of the '883 patent is activated whenever the engine brake is activated.
Although the braking system of the '883 patent may be utilized to decrease the travel speed of a vehicle, it may be inefficient in some situations. For example, when braking the vehicle on moderate declining grades, the vehicle brakes, in combination with the engine brake, may be adequate to satisfactorily stop the vehicle without the use of an additional parasitic load on the engine. However, because the cooling fan of the braking system disclosed in the '883 patent is activated whenever the engine brake is activated, the disclosed braking system may utilize vehicle resources to operate the cooling fan even though supplemental retarding is not necessary.
The disclosed retarding system is directed to overcoming one or more of the problems set forth above.